A menu is the navigation that shows to the left of a WordPress website, and allows users to navigate the site.
You can edit this menu by going into Appearance on the Dashboard. Menu is in the submenu of the Appearance menu.
If you have added a new page to your site, then you can add it to the menu by clicking the corresponding check box, then clicking “Add to Menu.”
You can then order the hierarchy of the menu items by dragging and dropping up and down, left and right. Dragging a page to the right makes the page a submenu to the page above. Once your are done, click “Save Menu.”
Now check your website, the menu should now be updated.